Abstract: The rectangular heat source model was used for modeling and numerical simulating the grinding surface temperature field under small depth of cut. The 45 steel was chosen as workpriece material, and the surface temperature distributions and characteristic microstructure were studied under different grinding parameters. The results showed that the maximum temperature of the grinding area increases with increasing the grinding depth or decreasing the workpiece rate under small depth of cut. The effect of grinding depth on the maximum surface temperature is greater than that of workpiece rate. While the effect of workpiece rate on the surface temperature gradient is greater than that of grinding depth. The temperature does not fully reach the transition point in the grinding zone.